1. Field of the Invention
The present invention relates to a thin film transistor having an organic semiconductor layer and an electronic device using the thin film transistor.
2. Description of Related Art
Recently, a thin film transistor (TFT) using an organic semiconductor layer as a channel layer, called organic TFT, has been noticed. The organic TFT allows the channel layer to be formed by a coating method, leading to reduction in manufacturing cost. In addition, since the channel layer may be formed at low temperature compared with that formed by an evaporation method, the organic TFT may be mounted on a flexible plastic film having low heat resistance.
The organic TFT is investigated to be used as a switching element for an electronic device such as a display device in the same way as previous inorganic TFT using an inorganic semiconductor layer as a channel layer, and has an organic semiconductor layer, and a source electrode and a drain electrode connected to the organic semiconductor layer.
The organic TFT is classified into a top contact type or a bottom contact type depending on a positional relationship of the organic semiconductor layer to the source and drain electrodes in the same manner as the inorganic TFT. In particular, the top contact type is regarded as promising since the source and drain electrodes are disposed to lie on the organic semiconductor layer, leading to reduction in contact resistance between the organic semiconductor layer and the source and drain electrode, and improvement in mechanical stability of the layer and the electrode.
Meanwhile, the top contact type has a difficulty where since the organic semiconductor layer has a low resistance to organic solvents, microfabrication using organic solvents is hardly performed without damaging the organic semiconductor layer in a step of forming the source electrode and the drain electrode.
However, proposal is recently made on a method of forming the source electrode and the drain electrode on the organic semiconductor layer by using a liftoff method (for example, see Japanese Unexamined Patent Application Publication No. 2008-085200).